Plasma treatment of conductive layers

ABSTRACT

A method for modifying the surface properties such as work function of semiconducting and conducting layers by plasma treatment. Also disclosed are electrical devices such as organic light emitting devices of enhanced performance owing to the use of plasma treatment-modified semiconducting or conducting layers.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.60/019,657, filed Jun. 12, 1996.

FIELD OF THE INVENTION

This invention relates to the field of organic optoelectronics, and moreparticularly to the enhancement of optoelectronic performance by thetreatment of conductive layers used in optoelectronic devices.

BACKGROUND OF THE INVENTION

Organic light emitting devices (OLEDs) make use of organic thin filmmaterials which emit light when excited by electric current. Thesedevices usually consist of a sandwich structure with organic thin filmsdeposited onto a transparent substrate and covered by top metal cathodecontacts. Between the transparent substrate and the organic thin filmsis a layer of transparent, conducting material which serves as an anode.

The organic thin films typically consist of an emission layer between ahole transporting layer and an electron transporting layer. When currentis applied between the cathode and anode, the emission layer provides arecombination site for electrons injected from the electron transportinglayer and holes from the hole transporting layer. This recombinationresults in the emission of light having a characteristic wavelengthdepending on the organic materials used. Alternatively, single-layerorganic or organic blend layers can be used instead of such multilayerorganic thin film systems.

Because of its transparency, high conductivity and efficiency as a holeinjector into organic materials, indium-tin-oxide (“ITO”) is widely usedas the anode material in OLEDS. Because the organic thin films are indirect contact with the ITO in OLEDs, the surface properties of ITO areexpected to directly affect the characteristics of these devices.Consequently, ITO layers which are not properly cleaned or have otherimperfections can result in poor device performance, such as shorting,unstable I-V characteristics, higher drive voltages and poorreliability.

To minimize the possibility of poor device performance due to the ITOlayer, conventional ITO treatments usually include combinations ofcleaning steps, such as sonification, boiling and rinsing in materialssuch as detergents, deionized (“DI”) water and organic solvents, anddegreasing in organic solvent vapor. Such cleaning techniques, however,are not often sufficiently reliable or reproducible, and consequently,irregular variations in device performance often occurs.

SUMMARY OF THE INVENTION

The present invention provides a method for modifying the surfaceproperties, such as chemical composition, work function, cleanliness androughness, of semiconducting or conducting layers by plasma treatment.The present invention also provides for electrical devices of enhancedperformance owing to the use of plasma treatment-modified semiconductingor conducting layers.

In one embodiment of the invention, a plasma treatment is used to modifyat least one of the conductive layers used in an OLED. This deviceperformance is greatly enhanced by the plasma treatment.

One advantage of the present invention is that it provides a reliablemethod for providing conductive layers of desired work function,cleanliness and performance.

Another advantage of the present invention is that it provides areliable method for providing electrical devices, and particularlyOLEDs, of enhanced performance.

Yet another advantage of the present invention is that it provideselectrical devices, and particularly OLEDs, having enhanced performance.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic flowchart showing the steps for fabricating anOLED in accordance with the present invention.

FIG. 2 shows I-V characteristics for OLEDs having plasma treated ITOlayers.

FIG. 3 shows the brightness-current and brightness-voltagecharacteristics for OLEDs having plasma treated ITO layers.

FIG. 4 is a plot of OLED brightness as a function of time for plasmatreated ITO compared to untreated ITO.

FIG. 5 shows compositional profiles for plasma treated ITO layers.

DETAILED DESCRIPTION

The present invention makes use of a plasma treatment to modify thesurface of conductive layers used in electrical devices such as OLEDs.By including such a plasma treatment to conductive layers, OLEDperformance is greatly enhanced in terms of qualities such as I-Vcharacteristics, drive voltages, efficiency and reliability. Theconductive layers in OLEDs are typically materials such as ITO, Pt, Al,Ag, Au, Mg, Mg/Ag, and Li/Al. ITO and Pt are the preferred materials fortransparent and reflective anode conductive layers, respectively.

The present invention includes a method for making OLEDs of enhancedperformance. As shown in FIG. 1, the first step in making OLED 100 isdepositing conductive layer 10 onto substantially transparent substrate11 to serve as an anode. Conductive layer 10 is substantiallytransparent and is preferably made of ITO. Substrate 11 can be made ofany suitable transparent material, such as quartz, sapphire, plastic, orpreferably glass. The preferred method of depositing the ITO layer 10 isby electron-beam evaporation or sputtering. After ITO layer 10 isdeposited onto substrate 11, the ITO is cleaned by wet cleaning steps indetergents, water or solvents as is known in the art. Suitabledetergents for cleaning ITO layer are known in the art, althoughTERGITOL™ (J.T. Baker Co.) is preferred. Suitable solvents includeacetone, methanol and preferably trichloroethane (“TCA”). It ispreferred that this step include cleaning by swabbing and sonificationwith TERGITOL, rinsing in DI water, degreasing by flushing in warm TCA,and finally rinsing in acetone and methanol.

After cleaning, ITO layer 10 is subjected to a plasma treatment. The gasused in the plasma treatment can be oxygen, hydrogen, argon, or gasmixtures containing these species, for example. Oxygen plasma, whichtends to increase ITO work function, is the most preferred plasma forOLED applications. This step can be carried out in either a barrel-typeplasma system or a parallel-type plasma system, as are known in the art.Power densities used during the plasma treatment range from 25 to 200mW/cm². There is no intentional heating of the sample during the plasmatreatment.

Organic layers 12 are deposited onto ITO layer 10 after the plasmatreatment. The organic material chosen for deposition will depend on thecolor or combination of colors desired for use. For example, if blue isthe desired emission color, the emissive layer of OLED is made from anysuitable blue light-emissive organic compound such as, for example,trivalent metal quinolate complexes, Schiff base divalent metalcomplexes, metal acetylacetonate complexes, metal bidentate ligandcomplexes, bisphosphonates, metal maleontriledithiolate complexes,molecular charge transfer complexes, aromatic and heterocyclic polymersand rare earth mixed chelates. The metal bidentate complexes have theformula MDL⁴ ₂ wherein M is selected from trivalent metals of Groups3-13 of the Periodic Table and Lanthanides. The preferred metal ions areAl⁺³, Ga⁺³, In⁺³ and Sc⁺³. D is a bidentate ligand such as2-picolylketones, 2-quinaldylkentones and 2-(o-phenoxy) pyridineketones. The preferred groups for L⁴ include acetylacetonate, compoundsof the formula OR³R wherein R³ is selected from Si and C, and R isselected from hydrogen, substituted and unsubstituted alkyl, aryl andheterocyclic groups; 3,5-di(t-bu) phenol; 2,6-di(t-bu) phenol;2,6-di(t-bu) cresol; and H₂Bpz₂. By way of example, the wavelengthresulting from measurement of photoluminescence in the solid state ofaluminum (picolymethylketone) bis [2,6-di(t-bu) phenoxide] is 420 nm.The cresol derivative of this compound also measured 420 nm. Aluminum(picolylmethylketone) bis (OsiPh₃) and scandium(4-methoxy-picolylmethylketone) bis (acetylacetonate) each measured 433nm, while aluminum [2-(O-phenoxy)pyridine] bis [2,6-di(t-bu) phenoxide]measured 450 nm.

Examples of green emissive layer OLED materials include tin (iv) metalcomplexes, such as those having the formula SnL¹ ₂L² ₂ where L¹ isselected from salicylaldehydes, salicyclic acid or quinolates (e.g.8-hydroxyquinoline). L² can be substituted and unsubstituted alkyl, aryland heterocyclic groups. When L¹ is a quinolate and L² is a phenyl, forexample, the tin (iv) metal complex will have an emission wavelength of504 nm.

Examples of red emissive layer OLED materials include divalent metalmaleonitriledithiolate (“mnt”) complexes, such as those described by C.E. Johnson et al. in “Luminescent Iridium(I), Rhodium(I), andPlatinum(II) Dithiolate Complexes,” 105 Journal of the American ChemicalSociety 1795 (1983). For example, the mnt [Pt (Pph₃)₂] has acharacteristic wavelength emission of 652 nm.

Additional OLED materials are known in the art (see, e.g., U.S. Pat. No.5,294,870 to Tang et al., entitled “Organic ElectroluminescentMulticolor Image Display Device”; Hosokawa et al., “Highly efficientblue electroluminescence from a distyrylarylene emitting layer with anew dopant,” 67 Applied Physics Letters 3853-55 (Dec. 1995); Adachi etal., “Blue light-emitting organic electroluminescent devices,” 56Applied Physics Letters 799-801 (Feb. 1990); Burrows et al.,“Color-Tunable Organic Light Emitting Devices,” 69 Applied PhysicsLetters 2959-61 (Nov. 1996)). The entire disclosures of these referencesare hereby incorporated by reference. Distyrylarylene derivatives suchas those described in Hosokawa et al. are a preferred class ofcompounds. Other preferred OLEDs are described in the copendingapplications discussed below.

After the organic layers 12 are deposited, conductive layer 13 isdeposited as a cathode layer to complete the OLED, as shown in FIG. 1.

The plasma treatment of semiconductive or conductive layers inaccordance with the present invention does not degrade the bulkproperties of these layers. Rather, the plasma treatment affects onlythe region at or near the layer surface, which in turn affects theperformance characteristics of the electronic device. It is thereforeconcluded that changes in device performance are related to the treatedsemiconductor or conductor surface properties.

The mechanism by which the plasma treatment affects OLED performance isnot presently known with certainty. While not wishing to be bound bytheory, however, it is suspected that the influence of the plasmatreatment on ITO surface work function has a significant effect on OLEDperformance. Other factors such as the removal of organic residue fromthe ITO surface and the reduction in surface roughness may alsoinfluence OLED performance.

The present invention is also applicable to so-called “top-emitting”OLEDs, in which emitted light is projected in a direction away from thesubstrate. In such devices, an anode layer is deposited onto asubstrate, with either of the anode layer or the substrate beingreflective. The organic layer(s) are then deposited over the anode, anda substantially transparent cathode is deposited over the organiclayer(s). The reflective anode is made of Pt, for example. In accordancewith the present invention, the anode is subjected to a plasma treatmentprior to the deposition of the organic layer(s). The plasma treatmenthas similar effects on the top-emitting device performance as it has onthe non-inverted device, namely an enhancement in I-V characteristics,drive voltages, efficiency and reliability.

The present invention is also applicable to OLEDs in which the locationof the anode and cathode about the organic layer(s) are reversed. Insuch devices, a plasma treatment is used to modify the surfacecharacteristics of the cathode layer before depositing the organiclayer(s).

The present invention is used to provide efficient, high brightness,monochromatic or multicolor, flat panel displays of any size. Thiswidens the scope of this invention to include displays as small as a fewmillimeters to as large as the size of a building. The images created onsuch displays could be text or illustrations in full color, in anyresolution depending on the size of the individual LED's. Displaydevices of the present invention are therefore appropriate for anextremely wide variety of applications including billboards and signs,computer monitors, telecommunications devices such as telephones,televisions, large area wall screens, theater screens and stadiumscreens. Embodiments of the present invention in which the emitted lightis directed in a direction away from the substrate are particularlyuseful for xerographic applications, as such embodiments allow for closepositioning to print paper without the use of lenses.

Although the present invention is described with specific reference toOLEDs, it may also be useful for other applications in which the surfacecharacteristics of semiconductor or conductor materials, such aschemical composition, work function, cleanliness and roughness, aremodified by plasma treatment.

The subject invention as disclosed herein may be used in conjunctionwith co-pending applications: “High Reliability, High Efficiency,Integratable Organic Light Emitting Devices and Methods of ProducingSame”, Ser. No. 08/774,119 (filed Dec. 23, 1996), now U.S. Pat. No.6,046,543; “Novel Materials for Multicolor LED's”, Ser. No. 08/850,264(filed May 2, 1997), now U.S. Pat. No. 6,045,930; “Electron Transportingand Light Emitting Layers Based on Organic Free Radicals”, Ser. No.08/774,120 (filed Dec. 23, 1996), now U.S. Pat. No. 5,811,833;“Multicolor Display Devices”, Ser. No. 08/772,333 (filed Dec. 23, 1996),now U.S. Pat. No. 6,013,982; “Red-Emitting Organic Light EmittingDevices (LED's)”, Ser. No. 08/774,087 (filed Dec. 23, 1996), now U.S.Pat. No. 6,048,630; “Driving Circuit For Stacked Organic Light EmittingDevices”, Ser. No. 08/792,050 (filed Feb. 3, 1997, now U.S. Pat. No.5,757,139; “High Efficiency Organic Light Emitting Device Structures”,Ser. No. 08/772,332 (filed Dec. 23, 1996),now U.S. Pat. No. 5,834,893;“Vacuum Deposited, Non-Polymeric Flexible Organic Light EmittingDevices”, Ser. No. 08/789,319 (filed Jan. 23, 1997), now U.S. Pat. No.5,844,363; “Displays Having Mesa Pixel Configuration”, Ser. No.08/794,595 (filed Feb. 3, 1997), now U.S. Pat. No. 6,091,195; “StackedOrganic Light Emitting Devices”, Ser. No. 08/792,046 (filed Feb. 3,1997), now U.S. Pat. No. 5,917,280; “High Contrast Transparent OrganicLight Emitting Device Display”, Ser. No. 08/821,380 (filed Mar. 20,1997), now U.S. Pat. No. 5,986,401; “Organic Light Emitting DevicesContaining A Metal Complex of 5-Hydroxy-Quinoxaline as A Host Material”,Ser. No. 08/838,099 (filed Apr. 14, 1997), now U.S. Pat. No. 5,861,219;“Light Emitting Devices Having High Brightness”, Ser. No. 08/844,353(filed Apr. 18, 1997), still pending; “Organic Semiconductor Laser”,(filed May 19, 1997), Ser. No. 08/859,468 (filed May 19, 1997), now U.S.Pat. No. 6,111,902; “Saturated Full Color Stacked Organic Light EmittingDevices”, Ser. No. 08/858,994 (filed May 20, 1997), now U.S. Pat. No.5,932,895; “An Organic Light Emitting Device Containing a Hole InjectionEnhancement Layer”, Ser. No. 08/865,491 (filed May 29, 1997), now U.S.Pat. No. 5,998,803; U.S. patent application Ser. No. 08/354,674, nowU.S. Pat. No. 5,707,745; Ser. No. 08/613,207, now U.S. Pat. No.5,703,436; Ser. No. 08/632,322, now U.S. Pat. No. 5,757,026; Ser. No.08/779,141, now U.S. Pat. No. 5,985,141; and Ser. No. 08/789,319, nowU.S. Pat. No. 5,844,363, each of which is also incorporated herein byreference in its entirety.

The present invention is further described in the following non-limitingexamples.

EXAMPLE 1

OLEDs having ITO layer anodes were fabricated according to the followingmethod.

ITO coated glass substrates were purchased from Donnelly Applied FilmsCo. The 1.1 mm thick polished glass was coated with a 200 Å SiO₂ barrierlayer and a 1400 Å ITO film. ITO was sputtered from an In₂O₃—SnO₂ (90 wt%-10 wt %) oxide target in an Ar/O₂ ambient at an elevated temperatureusing a planar dc magnetron sputtering system. The ITO was annealed insitu during the deposition and no post deposition annealing wasperformed.

Prior to their use, the ITO-coated glass substrates were cleaned byswabbing and sonification with detergent/DI water, rinsing in DI water,degreasing by flushing the ITO surface with convection flow in warm TCA,and finally rising in acetone and methanol. The substrates were thenused as cleaned or treated by using a plasma before deposition of theorganic layer. For the plasma treatment, the samples were exposed toplasmas of different gases in a parallel-plate type plasma reactorconfigured in the reactive ion etching mode. In this system, a rf powerof 25W corresponds to a power density of about 50 mW/cm².

The surface roughness of the plasma treated ITO layers, as measured byatomic force microscopy, was found to be 2.2 nm, 1.6 nm and 1.7 nm forthe as-grown, oxygen plasma, and hydrogen plasma treated ITO samples,respectively.

The organic materials deposited onto the ITO-coated glass substrateswere single-layer doped polymer devices in which the hole-transportmatrix polymer poly (N-vinylcarbazole) (“PVK”) contained dispersedelectron transport molecules, such as2-(4-biphenyl)-5(4-tert-butyl-phenyl)-1,3,4-oxadiazole (“PBD”) or tris(8-hydroxy quinolate) aluminum (“Alq”), and fluorescent dyes asefficient emission centers. PVK:PBD:coumarin 6 (“C6”) (100:40:0.3 byweight) was used for green devices, and PVK:Alq:nile red (100:40:0.2 byweight) was used for orange-red devices. These layers were deposited byspin-coating onto the ITO-coated glass substrates. The organic filmthickness was about 1050 Å.

After the polymer layers were deposited, top metal cathode contactsconsisting of 1200 Å Mg:Ag alloy and 800 Å Ag were deposited through ashadow mask with an array of 2 mm×2 mm holes. All spin-coating, deviceprocessing, including direct loading into the evaporator formetallization, and device characteristics were carried out under a drynitrogen atmosphere in a glove box.

FIG. 2 shows I-V characteristics for OLEDs having ITO layers which weretreated with different plasmas. FIG. 3 shows the correspondingbrightness-current and brightness-voltage characteristics, illustratingthe effect of plasma treatments on OLED efficiency. All forward I-Vcurves have two regimes, a low current regime with a weaker voltagedependence and a high current regime with a steeper current rise withvoltage. In all cases, the forward bias low current regime, referred toas “leakage,” is symmetrical to its reverse bias counterpart. Lightemission is observed only in the high current regime, referred to as the“bipolar” regime.

As can be seen from FIG. 2, the various plasma treatments considerablyaffect the turn-on voltage of the bipolar current, the leakage current,and the quantum efficiency. Devices made on cleaned as-grown ITO had aturn-on voltage of about 12V and an external quantum efficiency at 2.5mA/cm² of 0.28% photon/electron. The Ar plasma treatment reduced theturn-on voltage to 11V and increased efficiency to 0.35%. The oxygenplasma treatment dramatically reduced the turn-on voltage to 3V andincreased efficiency to 1%. On the other hand, the hydrogen plasmatreatment increased the turn-on voltage to 17V and reduced efficiency to0.007%.

A further consequence of improved OLEDs which include oxygen-plasmatreated ITO is an enhancement in reliability and maximum allowed currentbefore catastrophic breakdown. As shown in FIG. 4, the lifetime of anOLED made with oxygen-plasma treated ITO was found to be at least twoorders of magnitude longer than that of an OLED which included a cleanedas-grown ITO.

EXAMPLE 2

OLEDs were prepared as described in Example 1. Composition profiles ofthe ITO surfaces were obtained via Auger electron spectroscopy depthprofiling. As shown in FIG. 5, the as-grown ITO was Sn-rich andIn-deficient near the surface as compared to the bulk. The Sn:In atomicratio near the surface was about 1:3, while it was about 1:10 in thebulk. The oxygen plasma treatment lowered the ITO surface Sn:In ratio to1:6 and increased the surface oxygen concentration. The hydrogen plasmaalso reduced the Sn surface concentration, but substantially depletedthe surface oxygen concentration. This is evidence for anelectrochemical reduction-oxidation mechanism near the ITO surface inthe reducing hydrogen plasma and the oxidizing oxygen plasma,respectively.

The improvement in device performance resulting from the oxygen plasmatreatment, as described in Example 1, suggests that the surface chemicalcomposition might play a role in increasing the hole injection abilityat the ITO/organic layer interface. ITO is a heavily doped anddegenerate n-type indium oxide with both Sn dopants and oxygen vacanciescontributing to its conduction. The enhancement of hole injection maytherefore be due to an increase in the work function of the ITO as thesurface Sn:In ratio is decreased and the oxygen concentration isincreased. Ultra-violet photoemission spectroscopy measurements on theoxygen-treated ITO surfaces showed an increase in the work function ofabout 100-300 meV over the cleaned as-grown ITO surfaces. Ultra-violetphotoemission spectroscopy on the hydrogen-treated ITO surfaces showed adecrease in the work function of about 100 meV over the cleaned as-grownITO surfaces. Furthermore, the effects of the plasma treatments appearto be reversible. That is, an oxygen treatment following a hydrogentreatment produced results similar to those in which only an oxygentreatment was performed.

The present invention provides a reliable and effective method formodifying the surface properties such as work function of semiconductingor conducting layers by plasma treatment. When applied to OLEDs, thismethod results in significant enhancements in device performance whichhave not been previously known by the modification of conductive layersalone.

Those with skill in the art may recognize various modifications to theembodiments of the invention described and illustrated herein. Suchmodifications are meant to be covered by the spirit and the scope of theappended claims.

What is claimed is:
 1. An electrical device comprising a semiconductingor conducting layer having a work function modified by plasma treatment,said plasma treatment selected from the group consisting of treatmentwith an oxygen-containing species thereby increasing the work functionby about 100 to about 300 meV and treatment with a hydrogen-containingspecies thereby decreasing the work function by about 100 meV.
 2. Theelectrical device of claim 1 wherein said plasma treatment is with anoxygen-containing species thereby increasing the work function by about100 to about 300 meV.
 3. The electrical device of claim 1 wherein saidplasma treatment is with a hydrogen-containing species therebydecreasing the work function by about 100 meV.
 4. The electrical deviceof claim 1 wherein said layer is a substantially transparent conductor.5. The electrical device of claim 4 wherein said substantiallytransparent conductor is indium-tin oxide.
 6. The electrical device ofclaim 5 wherein said plasma treatment is an oxygen plasma treatmentthereby increasing the work function by about 100 to about 300 meV. 7.The electrical device of claim 5 wherein said indium-tin oxide layer hasan increased oxygen concentration at or near its surface.
 8. Theelectrical device of claim 1 wherein said layer is platinum.
 9. Anorganic light emitting device comprising: a plasma treated contactlayer; an organic layer over said plasma treated contact layer; and asecond contact layer over said organic layer, said plasma treatedcontact layer comprising a contact layer having a work function, whereinsaid contact layer is treated with a plasma treatment selected from thegroup consisting of treatment with an oxygen-containing species therebyincreasing the work function by about 100 to about 300 meV and treatmentwith a hydrogen-containing species thereby decreasing the work functionby about 100 meV.
 10. The organic light emitting device of claim 9wherein said plasma treated contact layer is the product of a plasmatreatment with an oxygen-containing species thereby increasing the workfunction by about 100 to about 300 meV.
 11. The organic light emittingdevice of claim 9 wherein said plasma treated contact layer is theproduct of a plasma treatment with a hydrogen-containing species therebydecreasing the work function by about 100 meV.
 12. The organic lightemitting device of claim 9 wherein said plasma treated contact layer isa substantially transparent conductor.
 13. The organic light emittingdevice of claim 12 wherein said substantially transparent conductor isindium-tin oxide.
 14. The organic light emitting device of claim 13wherein said plasma treated contact layer is the product of a plasmatreatment with an oxygen-containing species thereby increasing the workfunction by about 100 to about 300 meV.
 15. The organic light emittingdevice of claim 13 wherein said indium-tin oxide layer has an increasedoxygen concentration at or near its surface.
 16. The organic lightemitting device of claim 9 wherein said plasma treated contact layer isplatinum.
 17. A method of modifying a work function of a conductor orsemiconductor surface comprising: selecting plasma treatment appropriateto modify said work function; and subjecting said conductor orsemiconductor to said plasma treatment, said plasma treatment selectedfrom the group consisting of treatment with an oxygen-containing speciesthereby increasing the work function by about 100 to about 300 meV andtreatment with a hydrogen-containing species thereby decreasing the workfunction by about 100 meV.
 18. The method of claim 17 wherein saidplasma treatment is with an oxygen-containing species thereby increasingthe work function by about 100 to about 300 meV.
 19. The method of claim17 wherein said plasma treatment is with a hydrogen-containing speciesthereby decreasing the work function by about 100 meV.
 20. The method ofclaim 17 wherein said conductor is a substantially transparentconductor.
 21. The method of claim 20 wherein said substantiallytransparent conductor is indium-tin oxide.
 22. The method of claim 21wherein said plasma treatment is with an oxygen-containing speciesthereby increasing the work function by about 100 to about 300 meV. 23.The method of claim 21 wherein said indium-tin oxide layer has anincreased oxygen concentration at or near its surface.
 24. The method ofclaim 17 wherein said conductor is platinum.
 25. A method of making anorganic light emitting device comprising: providing a first contactlayer having a work function; treating said first contact layer with aplasma; placing an organic layer over said contact layer; and placing asecond contact layer over said organic layer, said step of treating saidfirst contact layer comprising treating said first contact layer with aplasma treatment selected from the group consisting of treatment with anoxygen-containing species thereby increasing the work function by about100 to about 300 meV and treatment with a hydrogen-containing speciesthereby decreasing the work function by about 100 meV.
 26. The method ofclaim 25 wherein said plasma treatment is with an oxygen-containingspecies thereby increasing the work function by about 100 to about 300meV.
 27. The method of claim 25 wherein said plasma treatment is with ahydrogen-containing species thereby decreasing the work function byabout 100 meV.
 28. The method of claim 25 wherein said first contactlayer is a substantially transparent conductor.
 29. The method of claim28 wherein said substantially transparent conductor is indium-tin oxide.30. The method of claim 29 wherein said plasma treatment is with anoxygen-containing species thereby increasing the work function by about100 to about 300 meV.
 31. The method of claim 29 wherein said indium-tinoxide layer has an increased oxygen concentration at or near itssurface.
 32. The method of claim 25 wherein said first contact layer isplatinum.
 33. The of electrical device claim 1, wherein said plasmatreatment is conducted at a power density ranging from about 25 to about200 mW/cm².
 34. The organic light emitting device of claim 9, whereinsaid plasma treated contact layer is subjected to a plasma treatmentconducted at a power density ranging from about 25 to about 200 mW/cm².35. The method of claim 17, wherein said plasma treatment is conductedat a power density ranging from about 25 to about 200 mW/cm².
 36. Themethod of claim 25, wherein said step of plasma treatment is conductedat a power density ranging from about 25 to about 200 mW/cm².
 37. Anapparatus incorporating the electronic device of claim 1, said articleselected from the group consisting of a computer, a television, abillboard, a sign, a vehicle, a printer, a telecommunications device, atelephone, and a copier.
 38. An apparatus incorporating the organiclight emitting device of claim 9, said article selected from the groupconsisting of a computer, a television, a billboard, a sign, a vehicle,a printer, a telecommunications device, a telephone, and a copier.